To continue the clinical characterization of patients with methylmalonic acidemia (MMA) and related disorders, a dedicated natural history study has been established. Our NHGRI protocol Clinical and Basic Investigations of Methylmalonic Acidemia and Related Disorders (ClinicalTrials.gov Identifier: NCT00078078) has enrolled >120 affected patients in the inpatient and outpatient settings and participated in over >300 patient/family visits to the NIH Clinical Center. Currently, the group affecteds evaluated under our clinical protocol at the NIH comprises one of the largest such patient cohorts in the world. In the past year, and compiled the first report delineating the neurocognitive phenotype seen in MMA patients OShea, C.J., Sloan, J.L., Wiggs, E.A., Pao, M., Gropman, A., Baker, E.H., Manoli, I., Venditti, C.P. #, Snow, J. Neurocognitive Phenotype of Isolated Methylmalonic Acidemia (MMA) (2012). Pediatrics. May 21. Epub ahead of print #corresponding author, PMID: 22614770, contributed reviews on propionic acidemia Carrillo-Carrasco N, Venditti C: Propionic Acidemia (May 2012) in: GeneReviews at GeneTests: Medical Genetics Information Resource database online. Copyright, University of Washington, Seattle, 1997-2010. Available at http://www.genetests.org. PubMed PMID: 22593918; Pena, L., et al, Natural history of propionic acidemia, Mol Genet Metab. 2012 Jan;105(1):5-9. PMID: 21986446; Sutton, V.R., et al, Chronic Management and Health Supervision of Individuals with Propionic Acidemia, Mol Genet Metab. 2012 Jan;105(1):26-33. PMID: 21963082; Chapman, K.A., et al. Acute management of propionic acidemia. Mol Genet Metab. 2012 Jan;105(1):16-25. PMID: 22000903; Schreiber, J., et al Neurologic considerations in propionic acidemia. Mol Genet Metab. 2012 Jan;105(1):10-5. PMID: 22078457and wrote a book chapter related to our clinical research focus Venditti C.P. and Berry, G.T. (in press) Inborn Errors of Metabolism and the Liver, in Nutrition in Pediatrics: Basic Science and Clinical Application 4th Edition, eds Watkins JB, Duggan C, Walker WA, eds.. A major advance has been in in a collaborative endeavor that elucidated the etiology of combined malonic-methylmalonic acidemia (CMAMMA) Sloan J.L., et al (2011) Exome sequencing identifies ACSF3 as the cause of Combined Malonic and Methylmalonic Aciduria. Nature Genetics. 14;43(9):883-6 PMID:21841779. This latter discovery has led to the identification of a new disease gene, ACSF3, and the delineation of a novel pathway for methylmalonic acid metabolism in man. Active efforts include the characterization of MMA patients who have received solid organ transplantation, neuroradiographic and spectroscopic studies on the MMA stroke syndrome, delineation of the ophthalmological manifestations of MMA and cobalamin disorders, the development of evidence-based dietary guidelines, and definition of the clinical phenotype of CMAMMA. A collaborative intra- and extramural grant application with Dr Mendel Tuchman (CNMC) to fund our initial studies using stable isotopes in MMA patients was submitted in November 2011 and selected for funding in 2012 (Metabolic Phenotyping in Methylmalonic Acidemia: Markers and Drug Response (2012-2014); Bench to Bedside Grant; Office of Rare Diseases Research, National Center for Advancing Translational Science; Role: co-PI). Laboratory investigations have focuses on generating and characterizing mouse models of methylmalonic acidemia and gene therapy studies. Because patients experience multisystemic manifestations involving tissues that are impossible to access for routine study, mouse models are needed to examine manifestations of the disease phenotype and to replicate tissue-specific pathology. The mechanisms underlying MMA-associated disease manifestations remain unknown. A major barrier is the ability to replicate the disease in mice. The development of new mouse models will allow disease mechanisms to be explored and new interventions tested. It is also anticipated that these mouse models may have general applicability to the wider study of related medical conditions, such as movement disorders, as well as environmental, nutritional, sporadic and inherited disorders that are associated with mitochondrial dysfunction. A murine model of MMA that approximates an orthotopic liver transplantation, Mut-/-;TgALBMut, has been created by transgenesis, using an albumin promoter and enhancer (ALB) to drive the expression of the wild-type Mut cDNA in hepatocytes of knock-out mice. Modeling of MMA renal disease in Mut-/-;TgALBMut mice has recently been accomplished and correlated with patient findings. To understand the pathogenic mechanism of these findings a genomic approach was undertaken to identify gene(s) expressed in the disease state and a number of differentially expressed transcripts were identified. One biomarker was validated with renal disease markers in the NIH cohort of 46 MUT MMA patients. A large team of intra- and extramural collaborators have contributed to this work and a manuscript detailing these studies has been submitted for publication. We plan to create additional murine models that have an physiologically apparent intermediate or inducible phenotype yet are robust to allow the assessment of gene therapy approaches and the exploration of pathophysiological mechanisms. We propose to use chronic dietary stress, acute environmental changes and/or pharmacogenomic manipulations, such as the interference with organic acid transport and glutathione depleting agents, to model life-threatening complications such as metabolic decompensation and stroke in these mouse models. We will then characterize the disease state using genomic, proteomic and metabolomic approaches to define mechanisms and identify biomarkers that might be translated to patient care. Other than routine dietary and cofactor therapy, no alternative to organ transplantation exists for patients with these inborn errors of metabolism. The successful demonstration of gene therapy for MMA is certain to provide precedence to treat many other disorders of intermediary metabolism, particularly those that feature mitochondrial localization of the metabolic lesion, using a similar approach. Building upon our success with various adeno-associated viral (AAV) vectors to deliver the murine methylmalonyl-CoA mutase gene, we have created a series of new AAVs suitable for potential translation to humans. Two have been created one that affords ubiquitous expression of the human MUT enzyme and another that directs hepatic expression. The ubiquitous expression vector has been studied in Mut-/- mice and dose reduction studies have established the minimum dose needed to rescue mice that display a neonatal lethal phenotype. A manuscript detailing these findings has been tentatively accepted for publication Chandler and Venditti, Pre-clinical efficacy and dosing of an AAV8 vector expressing human methylmalonyl-CoA mutase in a murine model of methylmalonic acidemia (MMA), Molecular Genetics and Metabolism, (accepted 9/2012), while experiments to characterize the liver specific expression cassette are ongoing. We will continue to determine the most effective dose and AAV vector for efficient gene therapy in a variety of MMA mouse models. Analysis of the effectiveness of each vector will use growth, metabolic, biochemical, expression and in vivo metabolic studies to determine the degree of correction achieved. It is anticipated that such pre-clinical studies will lead to the creation of an optimal vector for use in humans, affording an opportunity to pursue an IND submission to the FDA as a step toward translating gene therapy to the clinic.